(Well, I say "today" but it was originally published back on March 8, 1962.)
I'll be the first to admit that I probably haven't read as much Peanuts as I should -- especially given the sheer volume Schulz produced in his lifetime -- but I don't recall many in which he made active use of the comic strip format to comment on the strip itself.
What strikes me first is that there's very little in the way of comics here. We've got two heads talking. It could easily have been accomplished in one (admittedly long) panel, like so...
Although, by Scott McCloud's definition, we're no longer looking at a comic. There's no sequence.
Of course, that starts to ask the question of approach. What if the same art had been used throughout this particular strip?
In content, it's scarcely different. After all, Charlie Brown remains motionless in the original anyway, and Linus does nothing more than turn his head a couple times. But since we're seeing exactly the same thing throughout, the implication isn't any different than the single panel version. Does that mean it's not a comic (again, using McCloud's rarely disputed definition)?
Schulz didn't take this approach, though. (I daresay he would've considered it cheating.) He confirmed the panels do follow a series of actions, albeit minimal ones.
What this also does is highlight how unconcerned Charlie Brown is with the conversation. That he remains perfectly motionless throughout Linus' speech, despite Linus' obvious attempts at engaging in a discussion by repeatedly attempting to make eye contact. In Charlie Brown's estimation, the subject is not really worth worrying about.
Which brings us back to the meta-textuality of the joke. Schulz is using the strip to respond to concerns about comics being too driven by the text and not really being a marriage or words and pictures. He parodies the concern by using fairly minimal movements. And that he deliberately took the time to draw each panel separately and distinctly differently (two different poses, each shown from two different vantage points), he's shown that he's not saving himself any time or effort in his work. It's just as time consuming to draw someone standing as it is to draw someone kicking a football.
So Schulz's minimal changes to each panel actually serve multiple purposes here. Within the context of the comic itself, it highlights the character differences between the two kids. But at a meta-textual level, it reinforces the commentary on the subject of overly verbose comics.
You know, I'd never been a huge fan of Peanuts growing up, but the more I study the strips, the more impressed I become. Schulz's simplicity of line belies his sublime mastery of the craft.